Add a ring of warped text to the top of it, thickness = 1mm, height = 7mm. If it weren't text, but a solid cylinder it would have a volume of 0.8 cm^3. Since it is text, it should be a lot less than that. However the price for my original cylinder plus text ring is now $10.17, or a total of 5.4 cm^3, more than double the volume and cost of the plain cylinder alone.

If I add a ring of text around the original cylinder (not on top of it) so that the effect is embossed text raised 0.5mm, that should add much less than 0.4 cm^3 but it adds another 2.8 cm^3 or 2.9 cm^3 (I have two such embossed text rings).

So my final model is being priced at $20.91 when the price should be well less than $10. Probably less than $7.00.

I have never experienced a problem with volume miscalculations. They have always been bang on for me.

You should check the volume in your 3D program before you import your model into Shapeways. That will definately give you the answers you need to really know whether Shapeways is misculculating.

I always check my models in 3D Studio Max first, and they have always had exactly the same volumeXprice outcome.

If you are using Max, then select your model, click on the hammer icon which appears in right-hand windows, and then choose the measurement button. It will tell you the exact volume and measurements of your model.

I think i accidentally found the cause of this one.
a standard, 1x1x1 cube: 1 cm^3
a 1x1x1 cube, with a .9x.9x.9 cube inside it, with the smaller box having normals pointing in (i.e. a hollow cube).. lower price
the same two cubes, but with the normals on the smaller box pointing out (i.e. supposedly same as the first one.. filled, and some more filled): higher price.
that is: the price is higher than even the bounding box of the entire mesh.
and moving the smaller box out to beside the larger box the same price as if it was inside (although it would be more material)

it seems to be just adding up the sum of all manifold meshes, even if that means it is counting one region multiple times.

although i suspect this is probably error-prone or complicated to fix it to never double up, as a simple sanity check, the price should never be more than the price of the bounding box.

with your font example, i suspect it is putting multiple colliding meches inside each other, thus making one region be counted twice.

Xcapee: you may want to check out this script;
it's not only calculates volume but also checks for manifold errors and calculates Shapeways cost (with configurable markup etc).

Also I thought about your problem and another explanation could have been overlapping objects (if the volume of the text and the volume of the ring overlap they are counted twice, if that hasn't been fixed yet).